Scott Townley
Raritan, NJ

NX7U

I made a few changes to my Ten Tec Hercules II (model 420) solid-state amplifier.

First, the stock 0.093" Molex connector is not rated for 25A DC per contact...not even close. So that was the first thing to go. I nibbled out the back panel cutout for the original connector and replaced it with an Anderson SB120 with 4 AWG contacts.

4 AWG contacts are just the right size for 4 10-gauge wires. A red-black pair runs to each of 4 amplifier sub-assemblies. The original wires were 14-gauge.

I added an inline fuse for the remote control connection. As originally configured there is a 12 VDC unfused run that goes to the remote control for a "remote power on" function. Why it is unfused is beyond me, but it isn't anymore.

I also added a relay for the remote control "power on" function. The original design sent 12 VDC to a switch/relay combo in the remote control, then routed it back to the amp. The problem is that very 12 VDC line is then used in the amp for everything except the PA modules...for the fan, bias, relays, etc. If you have even a modest distance between the amp and remote control, the voltage drop was significant...the fan runs noticably slower and the bulbs dimmer. The relay coil is hooked into the 12 VDC return from the remote, then to ground...so "remote on" fires the relay. The contacts are just from "hot" 12 VDC to "fused" 12 VDC, which is the supply for everything but the PA (that's the 3AG glass fuse in front of the relay).

Finally, the insanely-large 0.02 ohm current-sense resistors were replaced by 0.005 ohm precision current-sense resistors. The Hercules uses high-side current sensing and detects faults due to inbalanced current draw (PA module failure) or excessive current draw. While a voltage drop is required to perform the current sensing, it also subtracts directly from the voltage available to the PA. Minimizing the voltage drop with a smaller resistor gives a bit more voltage to the PA while maintaining the fault detection capability.